Furnace



Patented June 3, 1947 FURNACE Percival B. Crocker, Foxboro, Mass.,assignorfto The Sentry Company, Foxboro, Mass., a corporation ofMassachusetts Appueeuen september zo, 1944, serle1Ne.ss4,9os

4 claims. (c1. 26a- 41) This invention relates to furnaces for the heattreatment oi metals and more particularly to one wherein the work isheated in a metal container (conveniently in the form of a metal tubetraversing the furnace) within which container a suitable atmosphere ismaintained about the work. The type of furnace with which the inventionis primarily concerned is one wherein the work. is heated attemperatures in the neighborhood or 2000 F. and ilnds a wide field ofapplication in the treatment of compacted metal powders in the practiceof powder metallurgy, so called, but also useful for other purposes, as,

for instance, brazing, silver soldering or bright annealing. An objectof the invention is to provide such a. furnace so constructed that theworkreceiving containers and other parts of vthe furnace are not liableto rapid deterioration.

My invention will be Well understood by reference to the followingdescription taken in connection with the accompanying drawings, where-Fig. I1 is a diagrammatic side elevation of' a furnace;

Fig. 2 is a central longitudinal section, the drawing being simplied bythe omission of a showing of details of construction not of importanceto an understanding of the invention; and.

Fig. 3 is a section on the line 3 3 of Fig. 2.

Referring to the drawings, the furnace there shown embodies a mainenclosure it constructed of :refractory brickwork on a suitable metallicframe, not .illustrated in detail, and which is divided by a tubularmember l2 of ceramic refreintory material traversing the same betweenopposed walls thereof and preferably, as hereinafter more fullydescribed, extending for a substantial distance beyond said walls. Thisreiractory tubular member I2 divides the interior of the enclosure intoan outer chamber which .may be traversed by heating elements I4 in theform of resistorrods of silicon carbide and an inner chamber I6corresponding to the space within the tube. Through the inner chamberand in spaced relation to the walls thereof extends a metal tube I8(which for reasons of economy may be ordinary mild steel), the interiorof which forms a work-treating chamber in which the pieces of work to betreated may be placed, conveniently being traversed therethrough onboats or trays. Suitable sealing means tting the tube I8 closes the endsof the inner chamber It. f

The tube I-8 may be provided with entrance and exit doors 2U and 22atits ends respectively which may be fitted with gas curtainsdiagrammatically indicated at 24. A portion of the tube between thefurnace proper and the exit door 22 may form 'a cooling chamber providedwith a water jacket 28. Hydrogen or cracked ammonia gas consisting of amixture of hydrogen and nitrogen may be supplied to the interior of thetube I8 at a point 21 adjacent the exit door 22 to flow through the tubefrom `left to right, viewing Fig. l, to be exhausted through a suitableport in or adjacent the entrance door 2li and serving to maintain adesired atmosphere around the pieces of work during'their treatment. Thefeatures referred to in this paragraph are in themselves conventional.

Referring now particularly to Figs. 2 and 3 of the drawing, I have thereshown the refractory tube I2 as provided with an interior lining' 28 ofcarbon. This lining may be in the form of a sleeve or a tube having asliding nt on the interior of the refractory tube I2 to permit its easyapplication or renewal. The lining may be sectional and I have herein inFig. 1 illustrated it as iff it were made of two sleeves, an openjoint30 being illustrated at the center of the furnace. A small exposure of aportion of the inner surface of the refractory tube I2 may be toleratedso long as it is free from cracks at the point of exposure. The drawing,Fig. 3, may be taken as showing a carbon sleeve lining about 1/2 inchthickin a refractory tube about 9 x 7 inches interiorly, which is anexample of a practical embodiment.

In 'the operation of the furnace the carbon, under the heat of theresistance elements It, is subject to partial combustion and generates agaseous mixture of nitrogen and the oxides of carbon, chiefly themonoxide, which lls the closed space I6 surrounding the tube t8 forminga stag nant atmosphere therein substantially neutral to the metal andwhich therefore protects it from deterioration.

I have found that best results are obtained if the refractory tube I2extends for a substantial distance beyond the walls of the mainenclosure i0 to regions of relatively low temperature, say about 1000"F. i

'I'he arrangement just described of a refractory tube projecting asubstantial distance beyond the furnace walls also facilitates thesealing of the chamber IS. Ordinary asbestos packing 32 may be tted tothe outside of the metal tube I8 and pressed against the end of the tubeI2, as by means of a clamping collar 3B, and will be effective andV longlasting'. 'I'he lining 2S may be terminated a short distance from theends of the refractory tube to yprovide for heat dissipation adjacentthe seal.

Refractcries such as are practical for use in constructing the tube I2are likely to develop cracks in use. In the construction shown therefractory tube may continue in service although cracked if not too muchdamaged. The atmosphere generated within the chamber I6 ls stagnant andunder substantially no pressure which would cause it to seep throughsmall cracks. Furthermore in normal use there is a layer of unconsumedcarbon lining the tube which tends to seal cracks and passagestherethrough. A long service from a given refractory tube may thus beobtained.

If gas should leak from the closed chamber i6 through the refractorytube l2 either because of the porosity of the latter or of slightcracks,the gas, as contrasted, for instance, with hydrogen, will notharm the silicon carbide resistors. The construction therefore permitsthe use of these highly satisfactory means for developing a high degreeof heat.

I am aware that the invention may be embodied in other specific formswithout departing from the spirit or essential attributes thereof, and ltherefore desire the present embodiment to be considered in all respectsas illustrative and not restrictive, as is in fact clear in severalmatters from the description itself. Reference is to be had to theappended claims to indicate those principles of the inventionexemplified by the particular embodiment described and which I desire tosecure by Letters Patent.

I claim: y

l. A furnace of the class described comprising an enclosure which isdivided by a refractory tube extending between opposite walls thereofinto an outer chamber in which heat is developed and an inner chamber, ametal tube extending through said inner chamber to provide awork-treating chamber in which work may beheated in a suitableatmosphere, means for sealing the ends of said inner chamber about themetal tube, the refractory tube having a sleevelike lining of carbonwherefrom is generated Within the refractory tube and about the metaltube a stagnant atmosphere consisting substantially of nitrogen andoxides of carbon and substantially neutral to the metal tube.

2. A furnace of the class described comprising an enclosure which isdivided by a refractory tube extending between opposite walls thereofinto an outer chamber in which heat is developed and an inner chamber, ametal tube extending through said inner chamber to provide awork-treating chamber in which work may be heated in a suitableatmosphere, means for sealing the ends of said inner chamber about themetal tube, the refractory tube extending substantially beyond the wallsof the enclosure to regions of relatively low temperature, therefractory tube having a substantially coextensive lining of carbonwherefrorn is generated within the refractory tube and about the metaltube a stagnant atmosphere consisting substantially of nitrogen andoxides of carbon and substantially neutral to the metal,

3. A furnace of the class described comprising an enclosure which isdivided by a refractory tube extending between opposite walls thereofinto an outer chamber in which heat is devel,- oped and an innerchamber, a metal tube extending through said inner chamber to provide aworktreating chamber in which work may be heated in a suitableatmosphere, means for sealing the ends of said inner chamber about themetal tube, and a lining for the refractory tube comprising one or moremovable sleeves of carbon slidably fitting the same, from which liningis generated Within the refractory tube and about the metal tube astagnant atmosphere consisting substantially of nitrogen and oxides ofcarbon and substantially neutral to the metal.

4. Heat treating apparatus wherein the work is enclosed in a metalcontainer to be heated in a suitable atmosphere therein and comprising aclosed chamber with refractory walls Within which the container isenclosed in spaced relation to said walls, the chamber having a liningof carbon, and means for heating the walls of said chamber exteriorly toprovide about the container a stagnant atmosphere of nitrogen and oxidesof carbon generated from the lining.

PERCIVAL B. CROCKER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,290,551 Gier July 21, 19421,700,942 Lederer Feb. 5, 1929 2,057,518 Fraser Oct. 13, 1916 2,375,463Berger May 8, 1945

